This invention relates to internal combustion engines and particularly the valve control of internal combustion engines that run on a four stroke cycle.
The majority of internal combustion engines used in motor cars, trucks and motorcycles operate on a four stroke cycle. The four stroke cycle internal combustion engine has been in use for the bulk of the 20th century. Over the years engine designers have constantly strived to improve the efficiency of such engines. In modern times these improvements in efficiency have dictated a need to also consider the environmental effects of the engine namely the production of pollutants including noxious gases that escape through the exhaust. Compromises have been reached in which the overall efficiency of the engine has been reduced by the need to introduce power absorbing equipment to purify the exhaust gases such as catalytic converters. Environmental issues have also dictated controls on fuels, consequently the addition of lead as an anti-knocking agent in high compression internal combustion engines has been phased out with the introduction of lead-free petrol resulting in further compromises in engine design.
Four stroke engines usually include at least one inlet and one exhaust valve per cylinder. In some small sophisticated engines pluralities of exhaust and inlet valves may be provided per cylinder. The valves are usually driven to an open position by the lobes of a camshaft. This drive can either be direct or indirect. The valves usually return to the closed position by the use of metal coil springs that simply urge the valve once open, back to the closed position. The size of spring force of the coil spring is designed to accommodate the engine when the largest demand is placed on the springs which is usually when the engine is running at the highest revolutions per minute (RPM). Thus, the valve springs have to be of sufficient size, weight and spring ratio to operate efficiently at the highest RPM. This means that at lower RPM the valve springs are too strong and thus unnecessary work is done against the springs causing a dramatic reduction in the engine efficiency in its normal operation range. Valve springs also have to be compressed during the starting procedure thus increasing the power required to tun over an engine to start it requiring large lead acid batteries and charging systems.
It is these considerations and the many problems discussed above that have brought about the present invention.
According to the present invention there is provided an internal combustion engine comprising at least one rotating, oscillating or reciprocating piston in a cylinder, each piston defining with the cylinder a combustion chamber, each combustion chamber having at least one inlet valve and one exhaust valve, and means to periodically open the inlet and exhaust valves, characterised in that the valves are closed by a gas spring pressurised by a source of gas pressure taken from each combustion chamber and monitored so that the closing force is proportional to the RMP of the engine.